RFID technology is one of many identification technologies in the automatic data identification industry. RFID market is growing sector of the radio technology industry, which brings together elements from many varied fields such as RF/microwave technology, semiconductor technology, telecommunications, data protection and cryptography, manufacturing technology, IT and many related areas.
Generally speaking a RFID system consists of two components, namely the transponder or tag, which is located on the object to be identified and the interrogator or reader, which may be a read or read/write device.
The heart of the RFID system lies in the transponder that carries information. The transponder responses to a coded RF signal received from the reader. Low cost and small size transponders are of most intense commercial interest. So-called passive transponder does not possess its own voltage supply. It is activated and functions when it is within the interrogation zone of the reader. As a passive transponder does not require a battery the cost of such transponder is usually low. However, a disadvantage of passive transponders is a short range.
The passive RFID transponder derives its energy (using an integrated rectifier) from the RF continuous wave interrogating signal and transmits the data by modulation of reflection cross-section (backscatter modulation).
Using current low power semiconductor technology, transponder chips can be produced with a power consumption of less than 5 μW. An efficiency of an integrated rectifier can be assumed to be 5-15% in UHF/microwave band. Therefore, an average received power of 50 μW is required at the terminal of the tag antenna for operation of the tag chip. In such a case, sufficiently high reader's transmitter power is required for the operation of the transponder chip.
In order to utilize the received power as effectively as possible, power matching should be provided. In case power matching is not provided, only part of the power is available to the rectifier (Schottky detector). Moreover, one should take into account the tag antenna matching losses including the fact that during altering the load (backscatter modulation) tag impedance is always changed. Thus, only a small proportion of incoming power is effective and circuit efficiency of the tag thereby is very low.
To send data from the transponder to the reader the input impedance of the transponder is altered in time with the data to be transmitted by the switching on and off additional impedance in time with the data to be transmitted. As a result, the power reflected by the transponder is modulated in time with the data. This procedure is known as modulated backscatter. Alternating the input impedance of the transponder results in the amplitude and/or phase modulation.
During backscatter the reader has permanently switched the transmitter on. Therefore, the sensitivity of the receiver in the reader is drastically reduced. In fact, for the transponder to be detected, the transponder's signal should be not more than 100 dB below the reader's carrier signal. The signal reflected by the transponder is modulated. In ASK (Amplitude Shift Keying) with a modulation index 100% the two sidebands would each contain 25% of the total reflected power, and in practice respectively less at a lower modulation index. As a result, it is difficult to achieve long operational distance between transponder and reader in passive transponder.
As is evident from what is said above, there are serious draw backs in the currently known systems. Hence, there is a clear need for a RFID system that could have long range of operation, low sensitivity to electromagnetic interference fields, high data security, high data rate, low cost, fast operation, and mobility.
The instant disclosure introduces solutions to the drawback of the currently known systems and provides a carrierless RFID system that possesses long range of operation, low sensitivity to electromagnetic interference fields, high data security, high data rate, low cost, fast operation, and mobility.